Rapidité de la vitesse d'altération des minéraux du sol en conditions ferrallitiques : méthode des minéraux-test

Les minéraux des sols sont soumis à des dissolutions et reprécipitations en fonction des conditions de milieu, et en particulier de l'activité biologique. Pour déterminer la cinétique des réactions mises en jeu dans le recyclage des éléments chimiques, des sachets de minéraux test contenant séparément de la gibbsite, deux types de kaolinite et un verre siliceux, ont été introduits dans les horizons supérieurs d'un sol ferrallitique de forêt amazonienne. Au bout de 6 mois, toutes les phases implantées ont été altérées, et d'autres minéraux, oxy-hydroxydes de fer et de titane, sont apparus. La réactivité des minéraux secondaires avec les conditions de milieu est donc rapide à l'échelle des temps pédologiques dans les sols étudiés. (Résumé d'auteur

Self-oscillations in field emission nanowire mechanical resonators: a nanometric DC-AC conversion

We report the observation of self-oscillations in a bottom-up nanoelectromechanical system (NEMS) during field emission driven by a constant applied voltage. An electromechanical model is explored that explains the phenomenon and that can be directly used to develop integrated devices. In this first study we have already achieved ~50% DC/AC (direct to alternative current) conversion. Electrical self-oscillations in NEMS open up a new path for the development of high speed, autonomous nanoresonators, and signal generators and show that field emission (FE) is a powerful tool for building new nano-components

Statistical properties of charged interfaces

We consider the equilibrium statistical properties of interfaces submitted to competing interactions; a long-range repulsive Coulomb interaction inherent to the charged interface and a short-range, anisotropic, attractive one due to either elasticity or confinement. We focus on one-dimensional interfaces such as strings. Model systems considered for applications are mainly aggregates of solitons in polyacetylene and other charge density wave systems, domain lines in uniaxial ferroelectrics and the stripe phase of oxides. At zero temperature, we find a shape instability which lead, via phase transitions, to tilted phases. Depending on the regime, elastic or confinement, the order of the zero-temperature transition changes. Thermal fluctuations lead to a pure Coulomb roughening of the string, in addition to the usual one, and to the presence of angular kinks. We suggest that such instabilities might explain the tilting of stripes in cuprate oxides. The 3D problem of the charged wall is also analyzed. The latter experiences instabilities towards various tilted phases separated by a tricritical point in the elastic regime. In the confinement regime, the increase of dimensionality favors either the melting of the wall into a Wigner crystal of its constituent charges or a strongly inclined wall which might have been observed in nickelate oxides.Comment: 17 pages, 11 figure

Genèse et fonctionnement des sols en milieu équatorial

La genèse des sols en milieu équatorial présente une forte composante biologique. La structure générale des profils ferrallitiques s'explique par le recyclage biologique des principaux éléments intervenant dans les équilibres minéraux-solutions, et la plupart des minéraux secondaires des sols ferrallitiques sont en rééquilibrage constant avec les conditions du milieu. La genèse des podzols est liée à une exportation précoce des composés organo-métalliques formés dans les horizons de surface, dépendante de la dynamique de l'eau à l'échelle des systèmes. (Résumé d'auteur

A modern Fizeau experiment for education and outreach purposes

On the occasion of the laser's 50th anniversary, we performed a modern Fizeau experiment, measuring the speed of light with a laser beam passing over the city centre of Marseille. For a round trip distance of almost five kilometers, the measurement has reached an uncertainty of about 10$^{-4}$, mainly due to atmospheric fluctuations. We present the experimental and pedagogical challenges of this brilliant outreach experiment.Comment: accepted by Eur J Phys in november 201

Научные подходы к диагностике социо-эколого-экономической устойчивости приморских регионов

На основе научных подходов предложена методика, позволяющая опреде-лить уровень социо-эколого-экономической устойчивости приморских ре-гионов. На основе использования системы показателей, характеризующих уровень социо-эколого-экономической устойчивости региона, сформули-рованы и предложены основные направления реализации методики опре-деления интегрального показателя уровня устойчивости приморской территории в социальном, экономическом и экологическом развитии.Based on the scientific approaches proposed technique allows to deter-mine the level of social, ecological and economic sustainability of coastal re-gions. On the basis of a system of indicators characterizing the level of social, ecological and economic sustainability of the region, formulate and propose guidelines implementation methodology for determining the integral indicator of the sustainability of the coastal territory in the social, economic and envi-ronmental development

Петрологічні дослідження в Україні: досягнення останніх десятиліть та нагальні проблеми

Викладено основні досягнення за останні 30–35 років українських геологів, в першу чергу — наукових працівників ІГМР ім. М. П. Семененка НАН України в області петрології. Висвітлені такі проблеми: 1 — метаморфізм, співвідношення грануліто-гнейсових і граніт-зеленокам’яних терейнів; 2 — чарнокіти; 3 — гранітоутворення та гранітоїдні формації; 4 — анортозит-рапаківігранітна формація; 5 — лужні породи; 6 — коматиїти; 7 — санукітоїди; 8 — метасоматоз; 9 — породоутворювальні та акцесорні мінерали; 10 — формаційний аналіз, петрологія та стратиграфія докембрію; 11 — фанерозойський магматизм; 12 — магматизм морського та океанічного дна; 13 — деякі нагальні проблеми.Изложены основные достижения за последние 30–35 лет украинских геологов, в первую очередь — научных сотрудников ИГМР им. Н. П. Семененко НАН Украины в области петрологии. Освещены такие проблемы: 1 — метаморфизм, соотношение гранулито-гнейсовых и гранит-зеленокаменных террейнов; 2 — чарнокиты; 3 — гранитообразование и гранитоидные формации; 4 — анортозит-рапакивигранитная формация; 5 — щелочные породы; 6 — коматииты; 7 — санукитоиды; 8 — метасоматоз; 9 — породообразующие и акцессорные минералы; 10 — формационный анализ, петрология и стратиграфия докембрия; 11 — фанерозойский магматизм; 12 — магматизм морского и океанического дна; 13 — некоторые насущные проблемы.Main achievements of Ukrainian geologists for the recent 30–35 years have been stated. In the first place the scientific results of petrologists of M. P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of NAS of Ukraine. The following problems have been elucidated: 1 — metamorphism; interrelation of granulite-gneissic and granite-greenstone terrains; 2 — charnokites; 3 — granite formation and granitoid formations; 4 — anorthosite-rapakivi-granite formation; 5 — alkaline rocks; 6 — komatiites; 7 — sanukitoids; 8 — metasomatosis; 9 — rock-forming and accessory minerals; 10 — formation analysis, petrology and Precambrian stratigraphy; 11 — Phanerozoic magmatism; 12 — magmatism of the sea and ocean bottom; 13 — some current problems

Mass balance of zinc redistribution during the pedogenesis of a soil developed on a natural geochemical anomaly

Pedogenetic processes that redistribute soil elements over time have been considerably investigated and clearly identified. Nevertheless, the quantification of their respective influences on element redistribution is still poorly known, while soil protection requires extensive knowledge of their long-time depending evolution. The quantitative redistribution of elements is of prime importance in polluted soils, since the long-term environmental hazards depend on their potential mobility and biodisponibility, thus speciation. Among the elements frequently encountered in polluted soils and exhibiting a well-established phytotoxic nature, zinc is of great concern. Nevertheless, pollutions are too recent to observe or even predict the long-term behavior of zinc in polluted soils. An alternative approach is to study paleosoil developed on natural geochemical anomalies. Indeed, such paleosoils display zinc concentrations equivalent to those of polluted soils with the advantage to involve long pedological time of contact between the elements and the different soil phases. Our study aims at quantifying the long-term redistribution of zinc during the pedogenesis of a soil developed upon a natural geochemical anomaly. We first determined zinc speciation both in the parental material and in the solum, then quantified redistribution by mass balance calculations. This approach permits to estimate Zn outputs or inputs in the solum and to quantify its redistribution along the profile and among the different mineral phases

Casimir force between two ideal-conductor walls revisited

The high-temperature aspects of the Casimir force between two neutral conducting walls are studied. The mathematical model of "inert" ideal-conductor walls, considered in the original formulations of the Casimir effect, is based on the universal properties of the electromagnetic radiation in the vacuum between the conductors, with zero boundary conditions for the tangential components of the electric field on the walls. This formulation seems to be in agreement with experiments on metallic conductors at room temperature. At high temperatures or large distances, at least, fluctuations of the electric field are present in the bulk and at the surface of a particle system forming the walls, even in the high-density limit: "living" ideal conductors. This makes the enforcement of the inert boundary conditions inadequate. Within a hierarchy of length scales, the high-temperature Casimir force is shown to be entirely determined by the thermal fluctuations in the conducting walls, modelled microscopically by classical Coulomb fluids in the Debye-H\"{u}ckel regime. The semi-classical regime, in the framework of quantum electrodynamics, is studied in the companion letter by P.R.Buenzli and Ph.A.Martin, cond-mat/0506363, Europhys.Lett.72, 42 (2005).Comment: 7 pages.One reference updated. Domain of validity of eq.(11) correcte